Tyrosinemia type III is a rare autosomal recessive disorder of tyrosine catabolism caused by a deficiency of 4-hydroxyphenylpyruvate dioxygenase. This disorder is characterized by neurologic findings including neurodevelopmental delay and/or intermittent ataxia. Liver damage, eye or skin findings have not been described.
Another rare disorder of tyrosine metabolism has also been attributed to mutations in the HPD gene, hawkinsinuria. Individuals with hawkinsinuria may be asymptomatic or exhibit failure to thrive, episodes of tyrosinemia and metabolic acidosis that respond to protein restriction. Symptoms improve within the first year of life. Patients with either disorder may be detected by newborn screening.